This thesis describes a new technique for studying the non-linear behaviour of reinforced concrete frames with flexible joints. The method is based on the concept of establishing an equilibrium deflected shape of a structure. The computations involve two basic levels of iteration. First, starting with an assumed nodal deformation, equilibrium deflected shapes and end forces of individual members in a structure are calculated using moment-thrust-curvature relations. The out of balance forces are computed by considering equilibrium of member forces at nodal points. In the second level of iteration based on a numerically computed nonlinear stiffness matrix, the nodal deformation are updated until the out of balance forces are negligible. The interaction of torsion with flexure has been assumed to be independent and further, the members are assumed to behave linearly in torsion. The influence of floors and cladding is ignored and only the skeleton frame is considered in the analysis. The associated computer program SWANSA based on the above method can be used as a design tool for sway and nonsway concrete frames with or without flexible joints. An interactive data entry facility allows the user to enter data by answering simple questions or by returning default values. Full scale experiments were carried out on eight column beam subframes to validate the computer program. Each subframe consisted of a two storey column with a short length of a typical mid-storey beam. Four types of connection commonly used in precast construction were selected to connect the beam to the column at mid height. Two sets of subframes were made for each connection, one each of a pair of subframes was tested for upward and downward rotations. The numerical technique is further validated with results published in literature, including experiments and the finite element method. All the comparisons show that the analysis developed in this thesis can be used to predict the behaviour of precast and other reinforced concrete frames for deflections, strains and for the ultimate loads. Finally, it is shown how a computer program based on the new numerical method can be used as an alternative method of designing rigid jointed or semi-rigid jointed precast concrete 3-dimensional frames, taking into account material and geometrical nonlinearities.